High pressure steam plant



May 2, 196] A. LIEBERHERR 2,982,267

HIGH PRESSURE STEAM PLANT Filed July 3, 1957 2 Sheets-Sheet 1 INVENTOR. A RTHU/F L IEBEEHEE/P.

A TTOEN E X 2 Sheets-Sheet 2 Filed July 3, 1957 Fig.2

INVENTOR. ARTHUR L/EBEPHE/PR.

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United States Patent HIGH PRESSURE STEAM PLANT Arthur Lieberherr, Winterthur, Switzerland, assignor to S ulzer Freres, S.A., Winterthur, Switzerland, a corporatron of Switzerland Filed July 3, 1957, Ser. No. 669,771 Claims priority, application Switzerland July 11, 19.56 '5 Claims. (Cl. 122-478) The present invention relates to high pressure steam plants, more particularly to a high pressure forced flow steam generator which is combined with a relatively low pressure steam resuperheater.

In steam generators of great capacity which produce the steam for operating a high pressure steam power plant,

' for example, in steam generators operating at the critical the combustion chamber they effect a desired lowering of the temperature of the combustion gases leaving the combustion chamber.

If the aforedescribed tube units form part of the evapcrating surface of the steam generator or of the high 35 pressure superheater surface of the steam generator, they do not present a source of difficulties. However, if the tube units are used for resuperheating relatively low pressure steam, the steam flowing through the tubes in the marginal zones of the units which are exposed to radiant heat and/ or which are hit first by the hot gases, may not carry away enough heat to effect proper cooling. of the tubes of the marginal portions of the unit. Burning of these tubes is unavoidable. It has been endeavored to overcome this difficulty by making the outer tubes of the unit shorter than the interior tubes to reduce the flow resistance and to increase the cooling effect of the outer tubes. In many cases this improvement is insufiicient. The arrangement of relatively short outer tubes cannot always be made without constructional difliculties.

It is an object of the present invention to provide an arrangement of the tube sections located in the outlet of the combustion chamber of a high pressure steam generator and forming at least a part of a relatively low pressureresuperheater, whereby these tube sections do not cause the problems described supra. According 'to the invention the tube sections located in the outlet of the combustion chamber and forming at least part of a steam resuperheater are at least partly shielded against excessive heating by tube sections in which the high pressure operating medium of the steam generator is heated. The tube unit or element located in the outlet of the combustion chamber is divided into two zones: One for heating the high pressure operating medium of the steam generator'and one for resuperheating relatively low pressure steam. Under otherwise equal conditions the factor of heat transfer increases substantially'proportionally with the pressure of the operating medium. The heat transfer through the tubes in which flows the high pressure operating medium is, therefore, always relatively great, even if the high pressure medium flows at a relatively little velocity. The endangered marginal or periph- Patented May 2, 1961 2 eral zone of the tube unit in the outlet of the combustion chamber can, therefore, be satisfactorily cooled by the high pressure operating medium. The interior sections of the unit which sections receive relatively little heat can 5 be suflicien'tly cooled by the relatively low pressure steam which must be resuperheated, although the heat transfer coefiicient is relatively small in the interior sections. Another advantage of the arrangement according to the invention is. that during starting of the steam generator or when operating at low load, suflicient high pressure operating medium is present for cooling the exterior zones of the tube unit which zones are most exposed to heat and the so shielded interior of the tube unit can be sufficiently cooled by expanded steam of which very little may be available during these periods.

In an embodiment of the invention at least the peripheral tubes of the heat absorbing element according to the invention form part of the high pressure superheater. However, thetubes most exposed to heat may form part of the evaporating section of the tube system of the steam generator. In some cases it may be preferred to use part of the section of the tube system of the steam generator in which the feed water is heated, which section is known as the economizer, for forming peripheral portions of the heat absorbing element which portions are exposed to the heat radiating from the combustion cham her and/ or to the relatively hottest gases emerging from the combustion chamber.

The novel features which are considered characteristic of the invention are set forth with particularity in the appended claims. The invention itself, however, and additional objects and advantages thereof will best be understood from the following description of embodiments thereof when read in connection with the accompanying drawing in which:

Fig. l is a diagrammatic sectional view of a steam generator and resuperheater according to the invention.

Figs. 2 and 3 are diagrammatic sectional views of modilied steam generators according to the invention.

Fig. 4 is a horizontal sectional view, looking downwards, of heat absorbing elements adapted to be placed in the outlet of the combustion chamber of a steam generator. 1

Fig. 5 is a side view of a heat absorbing element adapted combustion chamber of a steamgenerator'.

, Like parts are designated by like numerals in the dravw'ng.

Referring more particularly to Fig. l of the drawing, numeral 1 designates a forced flow once through steam generator heated by swivel burners 17. The liquid operating medium flows, as shown by arrows, from a conduit 2 through a distributor 5 into an economizer 3 and then through an evaporating tube section 4 which forms the lining of a combustion chamber 4'. The vapor pro- 0 duced in the section 4 is superheatedin a first superheater section 6 which is arranged in the flue of the steam generator above the economizer 3. The vapor is further superheated in a second superheater section 7 which forms the lining of the upper portion of the combustion chamber. The vapor emerging from the section 7 is collected in a header 19 and distributed into a third superheater section 8 which is also located in the upper part of the combustion chamber 4' and which forms marginal portions of a heating unit consisting of tubes placed in a plane. The hot combustion gases leave the combustion chamber through the aforesaid upper portion. The vapor from the tubes 8 is collected in a header 20 and distributed into the tubes of a final superheater section 9 which receives little or no heat by radiation and which is heated substantiallyby convection of heat from the hot combustion gases. The superheated vapor is directed from the section 9 into .a high pressureturbine 10. The vapor expanded in the turbine 10 is conducted through a pipe 11 into the first part 12 of a resuperheater which part consistsof closely spaced parallel tubes placed in a plane and forms a platen-like heat absorbing element having peripheral portions which are formed by tubes of the third superheater section 8 as described above. The relatively low pressure vapor flows from the resuperheater part 12 into a second resuperheater part 13 which receives heat by convection but can be so arranged, if desired, that it receives heat partly by radiation. The resuperheated vapor is conducted through the low pressure portion 14 of the turbine plantwhich drives an electric generator 15. The exhaust of the low pressure turbine 14 is condensed and returned to the vapor generator in the conventional manner. Numeral 18 designates a water separator interposed between the evaporating section 4 of the tube system of the generator and the first superheater section 6. If the generator is operated at the critical pressure of the operating medium or at a higher pressure, the water separator may be omitted. Numeral designates collectors or distributors interposed between individual sections of the tube system.

Whereas in the embodiment of the invention according to Fig. 1 peripheral portions of the tube unit element placed in the outlet of the combustion chamber are formed by tubes forming part of the high pressure superheater, the tubes of these peripheral portions form part of the evaporating section of the tube system of the vapor generator illustrated in Fig. 2. The tubes of the evaporating section 4 are connected with tubes 8' forming marginal portions of a tube unit or element placed in the outlet of the combustion chamber 4'. The tubes 8' constitute a second evaporating section, their outlets being connected with a water separator 18. The separated steam consecutively flows through superheater sections 6, 7 and 9 and then into the high pressure turbine 10. The exhaust of the latter flows, as in Fig. 1, through a first resuperheater section 12 which forms the inner part of a unit whose marginal portions are formed by the tubes 8'. Thereupon the steam flows through a second resuperheater section 13 and therefrom into the low pressure turbine 14.

In the embodiment of the invention diagrammatically shown in Fig. 3 tubes 8" forming marginal portions of a tube wall placed in the outlet of the combustion chamber 4 are connected with the economizer 3 and form part of the feed water heater. The liquid operating medium flows from the tubes 8" into the evaporating section 4, the water separator 18, and thereupon consecutively through the superheater sections 6, 7 and 9 and through the high pressure turbine 10. The rest of the circuit is the same as in the embodiments of the invention shown in Figs. 1 and 2.

Although Figs. 2 and 3 of the drawing show arrangements in which the operating medium passes through a single conduit through the steam generator, the invention is also applicable to arrangements in which a plurality of tubes are arranged in parallel relation with respect to the flow of the operating medium and/or in which the individual tube sections are composed of a plurality of tubes arranged in parallel relation with respect to the flow of the operating medium. The parallelly arranged conduits may be interconnected by headers or collectors at suitable points. The number of tubes arranged in parallel relation may be different in the different sections of the steam generator.

As seen in Fig. 4, the heat absorbing elements placed in the outlet of a combustion chamber are arranged in parallel planes and are spaced to facilitate the flow of the heating gas. The tubes 8 of Fig. l, 8 of Fig. 2, and 8" of Fig. 3 are exposed to the heat radiating from the combustion chamber and are impinged first by the hot 4 gases. The interior tubes of the elements which tubes form the resuperheating heating surfaces 12 are protected against radiant heat and receive relatively cool heating gases.

Figs. 5 and 7 illustrate two different arrangements of heat absorbing elements on whose outside are the tubes 8 in Fig. 1, 8' in Fig. 2 or 8" in Fig. 3 andon whose inside the tubes 12 are located. Fig. 6 shows an arrangement in which one side of a tube unit 8, 12 is adjacent to a wall and tubes 8 are arranged only on one side and on the bottom of the unit. In the three modifications shown in Figs. 5, 6 and 7 the tubes 8 and 12 are arranged in planes.

In the embodiment shown in Fig. 5, the lower part of the outer tube 8 is wound several times in serpentine fashion in a vertical plane. By arranging a suitable number of serpentine windings a desired amount of heat can be absorbed by the marginal tubes 8, the resuperheater tubes 12 still receiving the desired amount of heat.

Fig. 6 shows an arrangement of a bank of tubes placed in a plane, one side of the bank being adjacent to a wall of the combustion chamber. The tube 8 forming the marginal portion at the other side and at the bottom of the heat absorbing element is bent in hair pin fashion so that two tubes 8 protect the inner tubes 12 against the hot gases and heat radiating from the combustion chamber.

Fig. 7 shows a heat absorbing element in which two groups of resuperheater tubes 12 are arranged in parallel relation with respect to the flow of the steam to be resuperheated. The rwiperheater tubes of each group are bent like hair pins and are placed side by side and in the same plane to form a plane, plate-like panel. A distributor 21 is located above the center of the panel for distributing the steam to be resuperheated into the innermost of the tubes of a plurality of panels which are arranged in parallel planes. The resuperheated steam is collected in a collector 22 from the outer tubes 12 of a plurality of tube panels. The periphery of the individual heat absorbing elements is formed by a tube 8 which conducts high pressure operating medium and has the shape of a U as in the units shown in Figs. 1 to 3.

I claim:

1. In a steam generator operating on the reheat cycle, a combustion chamber, means for burning fuel in said combustion chamber for producing gases of combustion, a high pressure tube system absorbing heat from the burning fuel and from the gases of combustion for heating, evaporating and superheating a fluid passing through said tube system, a relatively low pressure tube system absorbing heat from the gases of combustion for reheating relatively low pressure steam passing through said low pressure tube system, said combustion chamber having an outlet portion for the combustion gases, and at least one heat absorbing element placed in said combustion chamber in front of said outlet portion and in substantially parallel relation to the flow of the combustion gases, said element including a plane, plate-like panel consisting exclusively of relatively low pressure heat absorbing tubes forming apart of said relatively low pressure tube system, said relatively. low pressure heat absorbing tubes having a plurality of straight, parallel portions, all of said parallel tube portions in the same panel being closely spaced and placed in a common plane in side by side relation, said heat absorbing element having a peripheral portion extending around said panel and being made of high pressure tubes forming part of said high pressure tube system, said high pressure tubes forming said peripheral portion being placed in the same plane as the tubes forming said panel and having substantially no heat exchange relation to said relatively low pressure tubes forming said panel.

' 2. In a steam generator as defined in claim 1 and Wherein said high pressure tubes forming said peripheral portion have straight portions extending normal to the straight, parallel tube portions in said panel.

3. In a steam generator as defined in claim 1 and wherein said high pressure tube system includes a high pressure superheater, the tubes forming said peripheral portion being interposed, for steam flow, in said high pressure superheater.

4. In a steam generator as defined in claim 1 and wherein said high pressure tube system includes a part in which water is converted into steam, the tubes forming said peripheral portion being interposed, for flow of the operating medium, in said part of said high pressure tube system in which part water is converted into steam.

5. In a steam generator as defined in claim 1 wherein said high pressure tube system includes an economizer in which 'water is heated prior to evaporation, the tubes forming said peripheral portion being interposed, for water flow, in said eoonomizer.

' References Cited in the file of this patent UNITED STATES PATENTS Kuppenheimer July 8, 1952 Hawley Jan. 8, 1957 Koch Dec. 9, 1958 Koch Apr. 21, 1959 FOREIGN PATENTS France Apr. 9, 1956 OTHER REFERENCES Combustion of August 1956 pages 47-56. 

